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About 10 μs after the Big Bang, the universe was filled—in addition to photons and leptons—with strong-interaction matter consisting of quarks and gluons, which transitioned to hadrons at temperatures close to kT = 150 MeV and densities several times higher than those found in nuclei. This quantum chromodynamics (QCD) matter can be created in the laboratory as a transient state by colliding heavy ions at relativistic energies. The different phases in which QCD matter may exist depend for example on temperature, pressure or baryochemical potential, and can be probed by studying the emission of electromagnetic radiation. Electron–positron pairs emerge from the decay of virtual photons, which immediately decouple from the strong interaction, and thus provide information about the properties of QCD matter at various stages. Here, we report the observation of virtual photon emission from baryon-rich QCD matter. The spectral distribution of the electron–positron pairs is nearly exponential, providing evidence for a source of temperature in excess of 70 MeV with constituents whose properties have been modified, thus reflecting peculiarities of strong-interaction QCD matter. Its bulk properties are similar to the dense matter formed in the final state of a neutron star merger, as apparent from recent multimessenger observation.

The HADES spectrometer currently operating on the beam of SIS18 accelerator in GSI will be moved to a new position in the CBM cave of the future FAIR complex. Electromagnetic calorimeter (ECAL) will enable the HADES@FAIR experiment to measure data on neutral meson production in heavy ion collisions at the energy range of 2-10 A GeVon the beam of the new accelerator SIS100. Calorimeter will be based on 978 massive lead glass modules read out by photomultipliers and a novel front-end electronics. Secondary gamma beam with energies ranging from 81 MeV up to 1399 MeV from MAMI-C Mainz facility was used to verify selected technical solutions. Relative energy resolution was measured using modules with three different types of photomultipliers. Two types of developed front-end electronics as well as energy leakage between neighbouring modules under parallel and declined gamma beams were studied in detail.

High-precision measurements of flow coefficients v n ( n = 1 - 4 ) for protons, deuterons and tritons relative to the first-order spectator plane have been performed in Au+Au collisions at s NN = 2.4  GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at the SIS18/GSI. Flow coefficients are studied as a function of transverse momentum p t and rapidity y cm over a large region of phase-space and for several classes of collision centrality. A clear mass hierarchy, as expected by relativistic hydrodynamics, is found for the slope of v 1 , d v 1 / d y ′ | y ′ = 0 where y ′ is the scaled rapidity, and for v 2 at mid-rapidity. Scaling with the number of nucleons is observed for the p t  dependence of v 2 and v 4 at mid-rapidity, which is indicative for nuclear coalescence as the main process responsible for light nuclei formation. v 2 is found to scale with the initial eccentricity ⟨ ϵ 2 ⟩ , while v 4 scales with ⟨ ϵ 2 ⟩ 2 and ⟨ ϵ 4 ⟩ . The multi-differential high-precision data on v 1 , v 2 , v 3 , and v 4 provides important constraints on the equation-of-state of compressed baryonic matter.

A precision measurement of the Z boson production cross-section at $\\sqrt{s}$ = 13 TeV in the forward region is presented, using pp collision data collected by the LHCb detector, corresponding to an integrated luminosity of 5.1 fb–1 The production cross-section is measured using $\\mathrm{Z}$ →$μ^+μ^-$ events within the fiducial region defined as pseudorapidity 2.0 < η < 4.5 and transverse momentum pT > 20 GeV/c for both muons and dimuon invariant mass 60 , M$_{μμ}$ < 120 GeV/c2. The integrated cross-section is determined to be $σ(Z → μ^+μ^-)$ = 196.4 ± 0.2 ± 1.6 ± 3.9 pb, where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measured results are in agreement with theoretical predictions within uncertainties.

The multihadron decays $Λ^0_b$ → $D+ρπ-π-$ and $Λ^0_b$ → $D^*+ρπ-π-$ are observed in data corresponding to an integrated luminosity of 3 fb-1, collected in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV by the LHCb detector. Using the decay $Λ^0_b$ → $Λ^+_cπ^+π^-π^-$ as a normalisation channel, the ratio of branching fractions is measured to be $\\frac {\\mathcal{B} ( Λ^0_b → D^+ρπ^-π^-)} {\\mathcal{B} (Λ^0_b → Λ^0_cπ^+π^-π^-)}$ x $\\frac{\\mathcal{B} (D^+ → K^-π^+π^+)} {\\mathcal{B}(Λ^o_c → ρK^-π^-)}$ = (%.35 ± 0.21 ± 0.16)%, where the first uncertainty is statistical and the second systematic. The ratio of branching fractions for the $Λ^0_b$ → $D^{*+}ρπ^-π^-$ and $Λ^0_b$ → $D^+ρπ^-π^-$ decays is found to be $\\frac {\\mathcal{B} ( Λ^0_b → D^{*+}ρπ^-π^-)} {\\mathcal{B} (Λ^0_b → D^+ρπ^-π^-)}$ X ($\\mathcal{B} (D^{*+}→ D^+π^0)$ + $\\mathcal{B} (D^{*+}→ D^+γ)$) = (61.3 ± 4.3 ± 4.0)%.

Searches for rare ${B}_s^0$ and $B^0$ decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb–1. Direct decays and decays via light scalar and $J/ψ$ resonances are considered. No evidence for the six decays searched for is found and upper limits at the 95% confidence level on their branching fractions ranging between 1.8 x 10–10 and 2.6 x 10–9 are set.

Mesons comprising a beauty quark and strange quark can oscillate between particle ($B^0_s$) and antiparticle ($\\bar{B}^0_s$) flavour eigenstates, with a frequency given by the mass difference between heavy and light mass eigenstates, Δms. Here we present a measurement of Δms using $B^0_s$ → $D^–_sπ^+$ decays produced in proton–proton collisions collected with the LHCb detector at the Large Hadron Collider. The oscillation frequency is found to be Δms = 17.7683 ± 0.0051 ± 0.0032 ps–1, where the first uncertainty is statistical and the second is systematic. This measurement improves on the current Δms precision by a factor of two. We combine this result with previous LHCb measurements to determine Δms = 17.7656 ± 0.0057 ps–1, which is the legacy measurement of the original LHCb detector.

Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb-1 collected with the LHCb detector, seven decay modes of the $B^+_c$ meson into a $J/ψ$ or $ψ(2S)$ meson and three charged hadrons, kaons or pions, are studied. The decays $B^+_c$ → $(ψ(2S)$ →J/$ψπ^+π^-$)$π^+$, $B^+_c$→$ψ(2S)π^+π^-π^+, B^+_c$→ J/$ψK^+π^-π^+$ and $B^+_c$ → J/$ψK^+K^-K^+$ are observed for the first time, and evidence for the $B^+_c$ →$ψ(2S)K^+K^-π^+$, decay is found, where J/ψ and $(ψ(2S)$ mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different $B^+_c$ decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.

Searches for CP violation in the two-body decays $D^{+}_{(s)}\\to h^{+} \\pi^{0}$ and $D^{+}_{(s)}\\to h^{+}\\eta$ (where h+ denotes a π+ or K+ meson) are performed using pp collision data collected by the LHCb experiment corresponding to either 9 fb–1 or 6 fb–1 of integrated luminosity. The π0 and η mesons are reconstructed using the e+e–γ final state, which can proceed as three-body decays π0 → e+e–γ and η → e+e–γ, or via the two-body decays π0 → γγ and η → γγ followed by a photon conversion. The measurements are made relative to the control modes $D^{+}_{(s)}\\to K^{0}_{S}h^{+}$ to cancel the production and detection asymmetries. The CP asymmetries are measured to be ACP(D+→π+π0)=(–1.3±0.9±0.6)%, ACP(D+→K+π0)=(–3.2±4.7±2.1)%, ACP(D+→π+η)=(–0.2±0.8±0.4)%, ACP(D+→K+η)=(–6±10±4)%, ACP(D$^{+}_{s}$→K+π0)=(–0.8±3.9±1.2)%, ACP(D$^{+}_{s}$→π+η)=(0.8±0.7±0.5)%, ACP(D$^{+}_{s}$→K+η)=(0.9±3.7±1.1)%, where the first uncertainties are statistical and the second systematic. These results are consistent with no CP violation and mostly constitute the most precise measurements of ACP in these decay modes to date.

A search for the$$ {B}_{\\mathrm{s}}^0 $$B s 0 → D *± D ∓ decay is performed using proton-proton collision data at centre-of-mass energies of 7, 8 and 13 TeV collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb − 1 . The decay is observed with a high significance and its branching fraction relative to the B 0 → D *± D ∓ decay is measured to be$$ \\frac{\\mathrm{\\mathcal{B}}\\left({B}_s^0\\to {D}^{\\ast \\pm }{D}^{\\mp}\\right)}{\\left({B}^0\\to {D}^{\\ast \\pm }{D}^{\\mp}\\right)}=0.137\\pm 0.017\\pm 0.002\\pm 0.006, $$ℬ B s 0 → D ∗ ± D ∓ B 0 → D ∗ ± D ∓ = 0.137 ± 0.017 ± 0.002 ± 0.006 , where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ratio of the$$ {B}_{\\mathrm{s}}^0 $$B s 0 and B 0 hadronisation fractions.